Ceramic composite doctor blade

ABSTRACT

It is an object to obtain a blade 1 with which coating or scraping can satisfactorily be performed and which is able to protect a plate-like member 3 from being broken. 
     A blade having a ceramic plate-like member 3 having an edge 3a and secured to the surface of an elongated metal plate 2 in the leading end portion of the elongated metal plate 2, wherein the blade 1 is deflected by 10 cm or more in the direction of the thickness thereof owning to the deadweight without breakage of the ceramic plate-like member 3 when the blade 1 is supported at two ends thereof which are apart from each other by 1 m or longer in the lengthwise direction thereof.

BACKGROUND OF THE INVENTION

The present invention relates to a blade for coating the surface of asheet-like member or that of a cylindrical member with another substanceor scraping off a substance from the surface of a member of theforegoing type.

Hitherto, doctor blades have been used in a variety of industrialfields. For example, the doctor blade has been used in a process forcoating the surface of paper with resin or a process for coating thesame with a heat sensitive material to manufacture heat sensitive paper,a process for coating the surface of sheet-like paper or another memberwith resin, a process for scraping off excess ink allowed to adhere tothe surface of a printing plate and a process for molding rubber orfoods into a sheet shape.

A major portion of the doctor blades has been made of a metal material,such as high-speed steel, and arranged in such a way that resin or thelike is spread while the resin or the like is being pressed by the edgeformed at the leading end of the doctor blade or ink or the like isscraped off. Doctor blades of a type made of a metal material howeversuffer from a problem in that inevitable wear of the edge of the doctorblade causes uniform coating to be impossible it leads to a fact thatthe doctor blade must be changed after it has been used for two hours,Thus there arises critical problems in that reliability and workingefficiency are unsatisfactory.

To solve the above-mentioned problems, a method has been disclosed inJapanese Patent Publication No. 2-38671, in which a hard film made oftungsten carbide (WC) is thermally sprayed to the end surface of theblade. However, the foregoing blade can be used in only short time ofabout 80 hours because the hard film is separated during the operation.

Accordingly, a structure has been suggested in which, as disclosed inJapanese Patent Publication No. 2-51398, at least the cutting part ofthe blade is made of zirconia ceramics.

When the overall body of the doctor blade or the cutting part of thesame is made of zirconia ceramics, the thickness must be considerablyreduced to 1 mm or smaller. Therefore, if the doctor blade is deflectedduring the operation, there arises a risk that the doctor blade will bebroken. If the blade is formed thick to prevent breakage, the bladecannot easily be deflected. In this case, there arise problems in thatcoating and scraping cannot easily be performed, thus resulting in thatcoating is performed nonuniformly and streaky defects take place.

In view of the foregoing, an object of the present invention is toprovide a blade which cannot be broken when the blade is deflectedduring operation or handling and which exhibits excellent wearresistance.

A blade according to the present invention comprises a ceramicplate-like member having an edge and secured to the surface of atelongated metal plate in the leading end portion of the elongated metalplate, wherein the blade is deflected by 10 cm or more in the directionof the thickness thereof owning to the deadweight without breakage ofthe ceramic plate-like member when the blade is supported at two endsthereof which are apart from each other by 1 m or longer in thelengthwise direction thereof.

In order to satisfactorily perform an operation using the blade, theblade must appropriately be deflected. A variety of studies wereperformed by the inventor of the present invention. As a result, apreferred result can be obtained by adjusting materials, dimensions andshapes of the metal plate and the ceramic plate-like member and bymaking the blade to be deflected by 10 cm or more in the direction ofthe thickness of the blade owning to the deadweight when the blade issupported at two ends thereof which are apart from each other by 1 m orlonger in the lengthwise direction thereof. Moreover, a structure inwhich the ceramic plate-like member is secured to the surface in theleading end portion of the metal plate enables the overall body of theblade to easily be deflected and the ceramic plate-like member to beprotected from being broken when the blade is deflected.

A blade according to the present invention comprises a ceramicplate-like member having an edge and secured to the surface of anelongated metal plate in the leading end portion of the elongated metalplate, wherein the apparent Young's modulus E_(A) (kg/cm²) of theoverall body of the blade is defined as follows:

    1/E.sub.A =V.sub.1 /E.sub.1 +V.sub.2 /E.sub.2

when the Young's modulus of the ceramic plate-like member is E₁ (kg/m²),the volume fraction of the same is V₁, the Young's modulus of the metalplate is E₂ (kg/m²) and the volume fraction of the sane is V₂, and thefollowing relationship is satisfied:

    5×10.sup.-10 <A<7×10.sup.-8

when the cross sectional secondary moment is I (m⁸), weight per unitlength is W (kg/m) and A=5W/384E_(A) I

That is, value A is a measure indicating the quantity of deflectionrealized by the deadweight of the blade. When the value A satisfies theabove-mentioned range, the blade can be deflected.

A blade according to the present invention comprises a ceramicplate-like member having an edge and secured to the surface of anelongated metal plate in the leading end portion of the elongated metalplate, wherein the following relationship is satisfied:

    E.sub.1 <3.0×10.sup.10

when the fracture toughness level of the ceramic plate-like member isK_(C) (kg/m^(3/2)), the Vickers hardness of the same is H (kg/m²), andthe Young's modulus of the same is E₁ (kg/m²), and the followingrelationship is satisfied:

    2.00×10.sup.-8 <R<2.60×10.sup.-8

when R=(E₁ /H)^(4/5) /(K_(C) ^(1/2) +H^(5/8)).

That is, the value R is the measure indicating the wear resistance. Whenthe value R satisfies the above-mentioned range, the blade hassatisfactory wear resistance and the same can appropriately be worn tobe fitted to the shape of the coated surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a perspective view showing a blade according to the presentinvention, and

FIG. 1(b) is a cross sectional view taken along line X--X shown in FIG.(a).

FIG. 2 is a cross sectional view showing a state where the bladeaccording to the present invention is used.

FIGS. 3(a) to 3(c) are cross sectional views showing another embodimentof the blade according to the present invention.

FIG. 4 is a diagram showing a method of measuring the amount ofdeflection of the blade according to the present invention.

EMBODIMENT

A blade for use in a paper making process will now be described as anembodiment of the present invention.

As shown in FIG. 1, a blade 1 according to the present invention has astructure formed by connecting a plate-like member 3 made of ceramics,such as zirconia, to the surface of a metal plate 2 made of high-speedsteel in the leading end portion of the metal plate 2 by using anadhesive agent 4. The plate-like member 3 has an edge 3a to enable theblade 1 to scrape off a coat material 5 while the blade 1 is spreadingthe coat material 5 on the surface of paper 6. Thus, the blade 1 is ableto apply the coat material 5 to the surface of the paper 6, as shown inFIG. 2.

Although not shown FIG. 1, a blade 1 according to the present inventionhas a structure formed by connecting a plate-like member 3 made ofceramics, to the surface of a metal plate 2 by using an adhesive agent4, the metal plate 2 is able to apply the coat material 5 on the surfaceof the paper 6. By the above structure. In a use initial stage, a metalplate 2 wear, and a metal plate 2 become the shape along the surfaceshape of the paper 6, the metal plate 2 is fit to the sape of thesurface shape of the paper 6, and a plate-like member 3 is exposed, thewear resistance is improved.

Since the blade 1 has a long overall length L of 1.5 m to 9 m, it ispreferable that the plate-like member 3 be integrally formed to have thesame length L. As an alternative to this the plate-like member 3 may besectioned into a plurality of portions each having an edge 3a in such amanner that the edges 3a are aligned after the plate-like member 3 hasbeen connected to the metal plate 2.

The metal plate 2 and the plate-like member 3 are joined together insuch a manner that the adhesive agent 4 is interposed between the flatportions of the metal plate 2 and the plate-like member 3. Note that thejoint structure between the metal plate 2 and the plate-like member 3may be realized in such a manner that the plate-like member 3 is, asshown in FIG. 3, joined to an inclined surface or a recess of the metalplate 2 with the adhesive agent 4. The edge 3a of the plate-like member3 is not always needed to be a sharp edge. As shown in FIG. 3, the edge3a may be formed into an in inclined shape or a curved shape.

When the blade 1 is used, the blade 1 must be deflected, as shown inFIG. 2. That is, when the blade 1 is deflected, the edge 3a of theplate-like member 3 can be pressed against the surface of the paper 6.Thus, the coat material 5 can be applied to have a uniform thickness andincreased contact strength.

Accordingly, the present invention has an arrangement such that astructure for joining the ceramic plate-like member 3 to the surface ofthe metal plate 2 in the leading end portion of the metal plate 2 ismainly composed of the metal plate 2. Thus, the blade 1 can easily bedeflected.

When deflection X realized due to the deadweight was measured toevaluate the deflection of the blade 1 in such a way that the blade 1was, as shown in FIG. 4, supported at the two ends of the blade 1 whichwere apart from each other by 1 m in the lengthwise direction of theblade 1, a fact was found that a satisfactory effect was obtained bymaking the deflection X to be 10 cm or more, preferably 20 cm or more.

If the deflection X is not smaller that 10 cm, preferably not smallerthan 20 cm, the blade 1 can sufficiently be deflected when the blade 1is used as shown in FIG. 2. Therefore, the edge 3a can be pressedagainst the surface of the paper 6 to cause the coat material 5 to havea uniform thickness and enable the contact strength to be increased.

The deflection X is determined in accordance with the materials, shapesand the dimensions of the metal plate 2 and the plate-like member 3.Therefore, the foregoing factors must be adjusted to make the deflectionX to satisfy the above-mentioned range. In actual, the deflection X issubstantially determined by the metal plate 2, which is the main portionof the blade 1. In an example case where the metal plate 2 is formed bythe high-speed steel, the thickness of the metal plate 2 is required tobe 1 mm or smaller.

The deflection X is the value measured when the blade 1 is supported atthe two ends which are apart from each other by 1 m. If the length ofthe blade 1 is not 1 m, the deflection is measured when the blade 1 issupported at the two ends thereof, and then the obtained value isconverted by a known method. If the blade 1 is longer than 1 m thedeflection X may be obtained by cutting the blade 1 and by supportingthe two ends.

An essential portion of the present invention lies in that the ceramicplate-like member 3 must be protected from being broken when the blade 1is deflected with the deflection X by the deadweight thereof, as shownin FIG. 4. When the blade 1 is used or transported, the above-mentioneddeflection X is realized if the worst comes to the worst. Even in theabove-mentioned case, the breakage of the plate-like member 3 must beprevented.

Therefore, the material, dimensions and the shape of the plate-likemember 3 are needed to be adjusted in such a manner that the plate-likemember 3 cannot be broken even if the deflection X is realized. Inparticular, the material of the plate-like member 3 is an importantfactor to prevent the breakage. Thus, ceramics having satisfactorystrength and toughness must be employed to make the plate-like member 3.Specifically, it is preferable that partially-stabilized zirconiaceramics be employed. The partially-stabilized zirconia ceramics areceramics mainly composed of ZrO₂ and containing one or more types ofstabilizers which are Y₂ O₃, MgO, CaO, CeO₂ and Dy₂ O₃. Thepartially-stabilized zirconia ceramics is in the form, the main portionof which is a tetragonal crystal phase. The zirconia ceramics of theforegoing type have significantly increased strength and toughnessbecause of stress-induced transformation thereof in which the tetragonalphase is changed into a monoclinic phase when stress is applied to thezirconia ceramics.

The material of the plate-like member 3 is not limited to zirconiaceramics. The required factors are such that the plate-like member 3 hasthe material, dimensions and the shape in such a manner that thedeflection X realized owning to the deadweight is 10 cm or greater andthe blade 1 cannot be broken when the blade 1 is supported at the twoends thereof as shown in FIG. 4.

In the present invention, when the Young's modulus of the ceramicplate-like member is E₁ (kg/m²), the volume fraction of the same is V₁,the Young's modulus of the metal plate is E₂ (kg/m²) and the volumefraction of the same is V₂, the apparent Young's modulus E_(A) (kg/cm²)of the overall body of the blade is defined as follows:

    1/E.sub.A =V.sub.1 /E.sub.1 +V.sub.2 /E.sub.2

Moreover, when the cross sectional secondary moment is I (m³), weightper unit length is W (kg/m) and A=5W/384E_(A) I, the followingrelationship is satisfied:

    5×10.sup.-10 <A<7×10.sup.-8

The value A is a measure indicating the quantity of deflection realizedby the deadweight of the blade 1. When the value A satisfies theabove-mentioned range, the blade 1 can be deflected.

In the present invention, when the fracture toughness level of theceramic plate-like member is K_(C) (kg/m^(3/2)), the Vickers hardness ofthe same is H (kg/m²), and the Young's modulus of the same is E₁(kg/m²), the following relationship is satisfied:

    E.sub.1 <3.0×10.sup.10

and when R=(E₁ /H)^(4/5) /(K_(C) ^(1/2) ·H^(5/8)), the followingrelationship is satisfied:

    2.00×10.sup.-8 <R<2.60×10.sup.-8

The reason why the Young's modulus E₁ is made to be smaller than3.0×10¹⁰ kg/m² lies in that the plate-like member 3 can easily bedeflected as the Young's modulus E₁ is made to be smaller to easilyfollow the deflection of the blade 1. If the plate-like member 3 caneasily be deflected, the edge 3a comes in contact with the paper 6 orthe like with uniform pressure. As a result, the thickness of theapplied film can be uniformed and the finished surface can be smoothed.

The value of R is a measure indicating the wear resistance. The wearresistance is improved in inverse proportion to the value of R. In acase of the doctor blade, the doctor blade must be somewhat worn in aninitial stage to be fit to the shape of the surface to be coated inorder to prevent uneven coated surface and generation of streaky defect.Therefore, appropriate wear resistance is required. In view of theforegoing, the following relationship must be satisfied:

    2.00×10.sup.-8 <R<2.60×10.sup.-8

In the foregoing case, satisfactory wear resistance can be realized andthus the lifetime of the blade 1 can be elongated.

The above-mentioned physical property values are measured by using testpieces made of the same material as that of the ceramics forming theblade 1 or test pieces obtained by cutting the blade 1 and each havingpredetermined dimensions. The Young's modulus E₁ is measured by asupersonic pulse method. The fracture toughness K_(C) is measured by anIF method, and the hardness H is measured by a Vickers hardness method.As an alternative to this, another measuring method may be employed if aknown converting equation is available with which the measured value isconverted.

Although the description has been performed about the blade for use inthe paper making process, the blade according to the present inventionmay be applied to a variety of purposes, for example, a process forcoating the surface of a wood or metal sheet member with resin or thelike, a process for scraping off ink allowed to adhere to the surface ofa printing plate and a process for molding rubber or foods into a sheetshape.

EXAMPLE 1

An example of the present invention was performed by manufacturing atest blade 1 shown in FIG. 1. The metal plate 2 was formed by high-speedsteel to have a thickness of 0.05 cm, a width of 7.5 cm and a length of100 cm. The plate-like member 3 was made of various ceramics shown inTable 1 and had a thickness of 0.1 cm, a width of 1 cm and a length of100 cm. The metal plate 2 and the plate-like member 3 were joined up byan epoxy adhesive agent 4.

In Table 1, "zirconia" is in the form of partially-stabilized zirconiaceramics which are mainly made of ZrO₂, which contain 3 mol % Y₂ O₃ andthe main portion of which is formed by tetragonal crystal. "alumina" isin the form of alumina ceramics composed of 99% Al₂ O₃ and a balancecomposed of SiO₂, MgO and the like, "silicon nitride" is in the form ofsilicon nitride ceramics mainly composed of Si₃ N₄ and containing Al₂ O₃and Y₂ O₃ as sintering agents and silicon carbide ceramics mainlycomposed of SiC and containing Al₂ O₃ and Y₂ O₂ as sintering agents.

The deflection X realized when each blade 1 was supported at the twoends which were apart from each other by 1 m as shown in FIG. 4 wasmeasured. Moreover, breakage of the plate-like member 3 in the foregoingstate was confirmed. Each of the ceramic products having theabove-mentioned dimensions was calculated in accordance with the Weibullstatistics. In addition, stress generated on the blade in a state wherethe two ends were supported as described above was obtained by using anequation for calculating stress which was generated under isotropicloads. In accordance with the obtained values, safety ratios werecalculated.

Results were as shown in Table 1. According to the results, thedeflection X of each blade 1 was a satisfactory amount of 22.7 cm.However, the plate-like members 3 respectively made of alumina, siliconnitride and silicon carbide were broken. On the other hand, theplate-like member 3 made of zirconia was not broken. The foregoingresults can as well as be estimated from calculations. In accordancewith experiments, the blade 1 can be used practically if the safetyratio is 2 or greater.

Therefore, a fact can be understood from this example that theplate-like member 3 made of zirconia ceramics is able to satisfactorilydeflect the blade 1 without breakage of the plate-like member 3.

                  TABLE 1    ______________________________________    Material of Plate-Like                Deflection          Generated Stress    Member      X (cm)    Breakage  (kg/cm.sup.2)    ______________________________________    Zirconia    22.7      No Breakage                                    2121    Alumina     22.7      Broken    3535    Silicon Nitride                22.7      Broken    3838    Silicon Carbide                22.7      Broken    3030    ______________________________________    Material of Plate-Like                Strength of Product    Member      (kg/cm.sup.2)                             Safety Ratio                                        Evaluation    ______________________________________    Zirconia    7200         3.4        ◯    Alumina     2232         0.63       X    Silicon Nitride                3600         0.94       X    Silicon Carbide                4320         1.42       X    ______________________________________

Example 2

As a comparative example, a metal plate 2 having a large thickness of0.11 cm was manufactured, and then a zirconia ceramics plate-like member3 was joined so that a blade 1 was manufactured. The blade 1 accordingto the comparative example was supported at the two ends as shown inFIG. 4. As a result, the plate-like member 3 was not broken. However,the deflection X was 5.7 cm which was smaller than 10 cm.

The blade according to the comparative example and the blade accordingto the Example 1 having the deflection X of 22.7 cm were subjected to anexperiment in which the coat material 5 was applied to the surface ofthe paper 6 as shown in FIG. 2 so that unevenness of the applied coatmaterial 5 was confirmed.

As a result, the operation using the blade according to the comparativeexample resulted in clear unevenness being confirmed, while theoperation using the blade according to the present invention resulted inthe coat material 5 being applied to have uniform thicknesses without nounevenness confirmed. The reason for this is that the blade 1 wasdeflected to press the edge 3a of the plate-like member 3 against thepaper 6. As a result, the coat material 5 was applied to have a uniformthickness.

A fact was understood that the coat material 5 was applied to haveuniform thicknesses by making the deflection X to be 10 cm or greaterwhen the blade 1 was supported at the two ends.

Example 3

Similarly to Example 1, blades 1 in each of which the plate-like member3 was made of zirconia ceramics and the metal plate 2 and the plate-likemember 3 were varied were manufactured.

Value A of each sample was calculated in such a manner that when theYoung's modulus of the ceramics forming the plate-like member 3 was E₁(kg/m²), the volume fraction of the plate-like member 3 with respect tothe overall body of the blade 1 was V₁, the Young's modulus of the metalplate 2 was E₂ (kg/m²) and the volume fraction of the metal plate 2 withrespect to the overall body of the blade 1 was V₂, the apparent Young'smodulus E_(A) (kg/cm²) of the overall body of the blade 1 is defined asfollows:

    1/E.sub.A =V.sub.1 /E.sub.1 +V.sub.2 /E.sub.2

Assuming that the cross sectional secondary moment is I (m⁸) and weightper unit length is W (kg/m²), the value A is expressed as follows:

    A=5W/384E.sub.A I

Then, the samples were subjected to experiments similar to thoseaccording to Example 2 to confirm unevenness of the applied coatmaterial 5 to evaluate the samples. If the value A satisfied thefollowing relationship as shown in Table 2:

    5×10.sup.-10 <A<7×10.sup.-8

the coat material 5 was applied to have uniform thickness withoutunevenness. The reason for this lies in that the blade 1 canappropriately be deflected if the value A satisfies the above-mentionedrange to press the edge 3a of the plate-like member 3 against the paper6, thus enabling the coat material 5 to be applied to have uniformthicknesses.

    ______________________________________    Thickness of            Thickness of    Metal Plate            plate-Like           Streaky Defect                                           Eval-    (mm)    Member (mm)                       Value of A                                 and Unevenness                                           uation    ______________________________________    0.05    0.5        2.3 × 10.sup.-7                                 Observed  X    0.10    0.5        5.7 × 10.sup.-8                                 Not Observed                                           ◯    0.25    0.5        9.1 × 10.sup.-8                                 Not Observed                                           ◯    0.50    0.5        2.3 × 10.sup.-8                                 Not Observed                                           ◯    0.75    0.5        1.0 × 10.sup.-8                                 Not Observed                                           ◯    1.00    0.5        .sup. 5.7 × 10.sup.-10                                 Not Observed                                           ◯    1.10    0.5        .sup. 4.7 × 10.sup.-10                                 Observed  X    1.20    0.5        .sup. 3.9 × 10.sup.-10                                 Observed  X    ______________________________________

Example 4

Then, the plate-like members 3 made of the various ceramics were used toexamine the wear resistance and uniformity of the applied coat material5. The metal plate 2 was made of high-speed steel to have a thickness of0.05 cm, a width of 7.5 cm and a length of 25 cm. The plate-like member3 was made of each of ceramics shown in Table 3 to have a thickness of0.05 cm, a width of 0.1 cm and a length of 25 cm. Then, the plate-likemember 3 was joined to the metal plate 2.

Among the ceramic materials shown in Table 3, zirconia 1 was the same aszirconia in Example 1, zirconia 2 was obtained by subjecting sinteredzirconia 1 to a hot isostatic pressing (HIP) process, zirconia 3 wasobtained by adding about 20% Al₂ O₃ to zirconia 1, after which the HIPprocess was performed, zirconia 4 was obtained by adding CeO₂ and Dy₂ O₃as stabilizer to the main component which was ZrO₂. Silicon carbide 2was mainly composed of β-SiC and arranged to contain B and C to serve assintering agents. Thermet was a combined-type sintered materialconsisting of a hard component, the main component of which was TiC, TiNand the like and iron family metal.

The respective blades were subjected to experiments in which the coatmaterial 5 was applied to the surface of the paper 6, as shown in FIG.2. After the experiment was performed for 150 hours, the state or wearof the edge 3a of the blade and the state of the applied coat material 5were observed.

The state of wear was evaluated in accordance with rearward movement ofthe edge 3a from the leading end because of the wear, while the state ofthe applied coat material 5 was evaluated such that existence of streakydefects on the surface of the paper was visually checked.

Results were as shown in Tables 3 and 4. As shown in Tables 3 and 4, thesamples having the value of R satisfying 2.00×10⁻⁸ <R<2.60×10⁻⁸ and theYoung's modulus E₁ of smaller than 3.0×10¹⁰ kg/m² resulted in free fromunevenness of the coat material 5. Therefore, a fact can be understoodthat samples satisfying the two factors enables the coat material to beuniformly applied and the lifetime to be elongated.

                  TABLE 3    ______________________________________    Material of             Toughness    Plate-Like             kc       Hardness Young's modulus    Member   (kg/m.sup.3/2)                      H (kg/m.sup.3)                               E.sub.1 (kg/m.sup.2)                                         Value of R    ______________________________________    Zirconia 1             6.8 × 10.sup.5                      1.25 × 10.sup.8                               2.1 × 10.sup.10                                         2.39 × 10.sup.-8    Zirconia 2             6.0 × 10.sup.5                       1.3 × 10.sup.8                               2.2 × 10.sup.10                                          2.5 × 10.sup.-8    Zirconia 3             7.0 × 10.sup.5                      1.35 × 10.sup.8                               2.6 × 10.sup.10                                          2.5 × 10.sup.-8    Zirconia 4             1.2 × 10.sup.5                       1.1 × 10.sup.8                               2.1 × 10.sup.10                                         2.16 × 10.sup.-8    Alumina  4.3 × 10.sup.5                      1.79 × 10.sup.8                               3.7 × 10.sup.10                                         2.83 × 10.sup.-8    Silicon Nitride             5.8 × 10.sup.5                       1.4 × 10.sup.8                               3.0 × 10.sup.10                                         2.83 × 10.sup.-8    Silicon  5.7 × 10.sup.5                      2.35 × 10.sup.8                               4.39 × 10.sup.10                                         1.92 × 10.sup.-8    Carbide 1    Silicon  3.5 × 10.sup.5                      2.35 × 10.sup.8                               3.79 × 10.sup.10                                         2.17 × 10.sup.-8    Carbide 2    Thermet  8.7 × 10.sup.5                      1.65 × 10.sup.8                               4.5 × 10.sup.10                                         2.62 × 10.sup.-8    ______________________________________

                  TABLE 4    ______________________________________    Material of               Evaluated Wear                           Unevenness of                                        Total    Plate-Like Member               Resistance  Surface of Paper                                        Evaluation    ______________________________________    Zirconia 1 ◯                           Not Observed ◯    Zirconia 2 ◯                           Not Observed ◯    Zirconia 3 ◯                           Not Observed ◯    Zirconia 4 ◯                           Not Observed ◯    Alumina    ◯                           Observed     X    Silicon Nitride               ◯                           Observed     X    Silicon Carbide 1               ⊚                           Observed     X    Silicon Carbide 2               ⊚                           Observed     X    Thermet    ◯                           Observed     X    ______________________________________

As described above, according to the present invention, there isprovided a blade comprising a ceramic plate-like member having an edgeand secured to the surface of au elongated metal plate in the leadingend portion of the elongated metal plate, wherein the blade is deflectedby 10 cm or more in the direction of the thickness thereof owning to thedeadweight without breakage of the ceramic plate-like member when theblade is supported at two ends thereof which are apart from each otherby 1 m or longer in the lengthwise direction thereof. Thus, the bladecan appropriately be deflected when the blade is used. Therefore,coating or scraping can satisfactorily be performed. Moreover, theplate-like member is not broken during use or transportation.

According to the present invention, thee is provided a blade comprisinga ceramic plate-like member having an edge and secured to the surface ofan elongated metal plate in the leading end portion of the elongatedmetal plate, wherein the apparent Young's modulus E_(A) (kg/cm²) of theoverall body of the blade is defined as follows:

    1/E.sub.A =V.sub.1 /E.sub.1 +V.sub.2 /E.sub.2

when the Young's modulus of the ceramic plate-like member is E₁ (kg/m²),the volume fraction of the same is V₁, the Young's modulus of the metalplate is E₂ (kg/m²) and the volume fraction of the same is V₂, and thefollowing relationship is satisfied:

    5×10.sup.-10 <A<7×10.sup.-8

when the cross sectional secondary moment is I (m⁸), weight per unitlength is W (kg/m) and A=5W/384E_(A) I. Since the blade canappropriately be deflected during use, coating or scraping cansatisfactorily be performed.

According to the present invention, there is provided a blade comprisinga ceramic plate-like member having an edge and secured to the surface ofan elongated metal plate in the leading end portion of the elongatedmetal plate, wherein the following relationship is satisfied:

    E.sub.1 <3.0×10.sup.10

when the fracture toughness level of the ceramic plate-like member isK_(C) (kg/m^(3/2)), the Vickers hardness of the same is H (kg/m²), andthe Young's modulus of the same is E₁ (kg/m²), and the followingrelationship is satisfied:

    2.00×10.sup.-8 <R<2.60×10.sup.-8

when R=(E₁ /H)^(4/5) /(K_(C) ^(1/2) ·H^(5/8)). Thus, the edge of theblade can satisfactorily be brought into close contact with a requiredmember. Moreover, the wear resistance of the blade can be improved.

What is claimed is:
 1. A blade comprising a ceramic plate-like member having an edge and secured to the surface of an elongated metal plate in the leading end portion of the elongated metal plate, wherein the blade is deflected by 10 cm or more in the direction of the thickness thereof owning to the deadweight without breakage of the ceramic plate-like member when the blade is supported at two ends thereof which are apart from each other by 1 m or longer in the lengthwise direction thereof.
 2. A blade comprising a ceramic plate-like member having an edge and secured to the surface of an elongated metal plate in the leading end portion of the elongated metal plate, wherein the apparent Young's modulus E_(A) (kg/cm²) of the overall body of the blade is defined as follows:

    1/E.sub.A =V.sub.1 /E.sub.1 +V.sub.2 /E.sub.2

when the Young's modulus of the ceramic plate-like member is E₁ (kg/m²), the volume fraction of the same is V₁, the Young s modulus of the metal plate is E₂ (kg/m²) and the volume fraction of the same is V₂, and the following relationship is satisfied:

    5×10.sup.-10 <A<7×10.sup.-8

when the cross sectional secondary moment is I (m³), weight per unit length is W (kg/m) and A=5W/384E_(A) I.
 3. A blade comprising a ceramic plate-like member having an edge and secured to the surface of an elongated metal plate in the leading end portion of the elongated metal plate, wherein the following relationship is satisfied:

    E.sub.2 <3.0×10.sup.10

when the fracture toughness level of the ceramic plate-like member is K_(C) (Kg/m^(3/2)), the Vickers hardness of the same is H (kg/m²), and the Young's modulus of the same is E₁ (kg/m²), and the following relationship is satisfied:

    2.00×10.sup.-8 <R<2.60×10.sup.-8

when R=(E₁ /H)^(4/5) /(K_(C) ^(1/2) ·H^(5/8)). 